Acoustic device



Sept. 28, 1954 S. E. LEVY ET AL 2,690,231

ACOUSTIC DEVICE Filed March 9, 1950 INVENTORS SIDNEY E. LEVY SAUL J. WHlTE -ABRAHAM B. COHEN BY THEIR ATTORNEYS Patented Sept. 28, 1954 ACOUSTIC DEVICE Sidney;Levy,- White Plains,= Saul :J; White, New Rochelle, and Abraham B. Cohen; Bronx; ,N; Y.',,

assignors to University Loudspeakers, 111%.,

White ,Plains, N; Y.', a corporation-ofNew-rYorka ApplicationMarch 9, 1950, Serial No'.'148,656

3' Claims. 1

This invention has tondo ,Withhorn-tYDe loudspeakers adapted. tov producewide-angle distribution of sound.

The horn-type loudspeaker of the. present in vention produces more uniform dispersion of sound over the area in the horizontal plane represented by a semi-circle in front of the speaker with greater signal amplitude than has previously been attained.

Conventional round horn-type loudspeakers produce a signal of maximum amplitude directly in front of the speaker but the amplitude cfthe signal decreases rapidly as the listener moves away from thecenterzaxis of-the speaker. As a result,- attempts have been made to design horns capable of producing, sound with'greater uniformity over a wide angle in the horizontal plane, but theseprior horns radiated-sound over:unnecessarily wide angles in the vertical plane: as well, and an excessive energy loss occurredso that dispersion of radiation: in, the horizontal plane was accomplished at the loss of considerable signal energy.

In the -horn-type loudspeaker of the present invention, sound radiation in-.the vertical plane is held to the minimum necessary and the signal energy thus conserved is utilized to expand the radiation in the horizontal plane. As a resuit, a relatively uniform signal can be maintained over a large are on either side of the center axis of the horn and of substantially greater amplitude than any previously attained in directional loudspeakers. This is accomplished by arranging the horn walls so that in the initial stage the acoustic signal is expanded in a vertical direction .at the desired rate and, during the final stage, the signal is expanded in the horizontal direction at the same rate. During the final stage, the lateral or top and bottom walls restrict the expansion of the wave in the vertical plane, thus building up pressure which increases the signal energy radiated in the horizontal plane.

In the accompanying drawings, Figure 1 is a perspective view of the horn;

Figure 2 is a vertical section taken along line 2-2 of Figure 1; and

Figure 3 is a horizontal section taken along line 3-3 of Figure 1.

The horn IE1 is connected to a conventional driver (not shown) through any convenient coupling, such as the neck i I with internally tapped threads. For best results, the internal diameter of the horn throat l5 should be the same as the diameter of the driver sound throat.

The cross-sectional area"of-the horn 10 from the throat I5 to themouthll increases at a predetermined rate, which may beat'anyof the expansion rates used in horn construction. The

1 exponential rate of 'expansionais thatmost commonly-employed, aformula for which is as follows:

Then

to simplify casting operations, may be provided with .a slight outward flare: An inward flare should be avoided when the horn is to be cast. Theang-l'e of divergence betweenthe lateral walls I2 is chosen so that the cross-sectional area of the horn will increase at the selected expansion rate. The first chamber is extended preferably to a point where the distance between the lateral walls is approximately one-third of the wave length of the desired cut-off frequency.

In the second chamber, the lateral walls 12b extend from the first chamber substantially horizontally or are slightly flared from the horizontal depending on circumstances to be described. On the other hand, the vertical walls [db in the second chamber are flared sharply as shown, the degree of flaring being chosen so that the crosssectional area in the second chamber will continue to expand at the selected rate. For best results, this second chamber should extend from the first chamber approximately one-third of the wave length of the desired cut-off frequency. If the preferred dimensions given above for the two chambers in relation to the cut-off frequency are utilized, the axial lengths of the two chambers are, as shown in the drawings, approximately equal.

Depending on the rate of expansion chosen and the cut-off frequency selected, it may not be possible to maintain this rate of expansion in the second chamber to its mouth merely by the flaring of the vertical walls, i. e. the curve of the vertical walls may become tangential to a crosssectional plane of the horn before the desired distance to the mouth has been reached. In that event, the lateral walls 12b may be slightly flared so as to have the flare of the vertical flanges reach a tangential point at the point where it is desirable to have the mouth of the second expansion chamber located while still maintaining the desired rate of expansion.

It will be observed that in the second chamber Where the lateral walls 121) are disposed horizontally or at most have only a slight flare, vertical expansion of the sound Waves is largely prevented and this restriction on vertical expansion builds up pressure which serves to add energy to .and aid the dispersion of the sound waves in a horizontal direction which, due to the flaring of the vertical walls Mb, is relatively unopposed.

As before observed, the cross-sectional area of the horn increases progressively at the selected rate throughout its entire length from the throat to the mouth of the horn. Although at the junction 15 of the two chambers there appears to be a break or discontinuity, there is no break or discontinuity in the rate of area increase throughout the horn length. The impression of discontinuity arises solely from the outward physical appearance of the horn and does not in fact exist a matter of air column expansion. As a result, the air column loading upon the diaphragm is uniform at all frequencies above the selected cuton frequency, and within this range standing waves or reflections within the horn caused by abrupt changes in horn loading are substantialiy avoided.

In the above description, the terms horizontal and vertical are used for the purposes of convenience to represent two planes .at right angles to each other. The point to be emphasized is .i the axis shown as 3-3 in Figure l, and referred to in the specification as the horizontal plane, constitutes the plane on which the widest dispersion of sound will take place regardless of the direction that this horn axis is placed with respect to the horizon.

1'. claim:

1. A loudspeaker horn for producing wide-angle distribution formed by vertical and lateral walls, in which for a portion of the horn the vertical walls are substantially parallel to each other and the lateral walls are inclined away from each other at an angle such that the cross-sectional area of said portion progressively increases at a selected rate, and for the remaining portion of the horn the lateral walls are substantially parallel to each other and the vertical walls flare outwardly at a rate such that the cross-sectional area of said remaining portion progressively increases at a selected rate, the axes of the two portions being straight and in alignment and the length of the axis of the second portion being approximately equal to the distance between the lateral walls at the exit from the first portion.

2. A loudspeaker horn for producing wide-angle distribution according to claim 1 wherein the rates of increase of the cross-sectional areas of the first and remaining portions respectively of the horn are substantially the same.

3. A loudspeaker horn for producing wide-angle distribution as claimed in claim 2, in which the distance between the lateral walls at the end of said first portion is approximately one-third of the desired cut-off frequency and in which said remainder of the horn extends from the end of said first portion a distance approximately onethird of the wave length of the desired cut-off frequency.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,314,980 Pognowski Sept. 2, 1919 1,477,556 Grissinger Dec. 18, 1923 1,689,009 Byrns Oct. 23, 1928 1,747,830 Harrison Feb. 18, 1930 1,754,425 Hinckley Apr. 15, 1930 2,537,141 Klipsch Jan. 9, 1951 FOREIGN PATENTS Number Country Date 775,561 France Jan. 4, 1935 

